In molded polyester polyurethane systems or systems using flame retardant, the hydrolytic stability of the system is very important. For example, in spray foams, polyester polyols and flame retardants are used because they can improve the fire performance of the final product but, upon storing a polyester polyol and flame retardant in the presence of water and tertiary amine, decomposition of the polyester to acid and polyol occurs causing the amine to form a salt. The tertiary amine catalyst becomes acid blocked reducing the reactivity of the system, often rendering it unsuitable for use. This problem is particularly serious in spray foams where systems with very high reactivity are required because the reaction mixture is expected to react very fast as it is sprayed over a surface. If the reactivity is decreased, the spraying mass of material cannot adhere to the surface causing it to drip or sag, and solidify at a different location than the spraying point. In addition, due to the high reactivity required in spray foams, high use levels of tertiary amines are required which combined with water present in the systems causes the polyester polyol to hydrolyze much faster than in other polyester systems.
Isocyanate reactive compositions containing polyester polyols for making polyurethane (PU) foam are typically mixed with water, flame retardants, amine catalysts, metal catalysts, surfactants and other additives for making polyurethane foams. Polyester polyol and flame retardants are characterized by their poor hydrolytic stability in such reactive compositions. Their hydrolytic instability is particularly enhanced in the presence of alkali such as tertiary amines which are normally present in the PU systems as catalysts.
The presence of tertiary amine catalysts causes the polyester polyol and flame retardant to hydrolyze to the corresponding glycols and acid causing the acid to neutralize the tertiary amine reducing the overall reactivity of the system which has serious implications on the kinetics and properties of the final product.